Importance of the Lunar Cycle on Mesopelagic Foraging by Atlantic Bluefin Tuna in the Upwelling Area of the Strait of Messina (Central Mediterranean Sea)

Abstract

The influence of the lunar cycle on bluefin tuna foraging in the upwelling area of the Strait of Messina was investigated by exploring trophic interaction with mesopelagic fish and cephalopod prey. To focus on how the lunar cycle could affect availability of mesopelagic prey for this predator, we tested potential differences in the diet related to each lunar phase. Moreover, we considered two potential impacts of the lunar cycle: the lunar irradiance and the strength of currents. Overall, 2672 prey items were mesopelagic fish and cephalopods, representing 60.7% of overall diet by number. The main mesopelagic fish prey items were lanternfishes and dragonfishes, while Onychoteuthis banksii was the most important cephalopod prey. In summary, the Strait of Messina has highly specific hydrodynamic and biological features which strongly depend on upwelling currents, which in turn are influenced by the lunar cycle (new and full moon with strong currents, quarters with fewer currents). Upwelling causes water mixing, bringing to the surface a large amount of mesopelagic fauna which become more readily available to tuna. Lunar irradiance contributes to the variation of prey composition, increasing the success of visual predation on mesopelagic resources at high light in the water column.

Stranding of Mesopelagic Fishes in the Canary Islands

“…Interestingly [ 30 , 57 ], in the Mediterranean Sea, it was also concluded that the new and full moon influenced the strength of the currents. Days before to the stranding, we observed a full moon (26 May 2021, Figure 5 A,C), which coincided with an increase in both the current and wind velocity during this period.…”

“…Stranded mesopelagic fishes have been recorded in Mediterranean waters along the Sicilian coast of the Strait of Messina (central Mediterranean) [ 23 , 24 , 25 , 26 ], providing important biological material for taxonomical studies since the eighteenth century [ 23 , 24 , 27 , 28 ]. Several studies of stranded species were carried out to relate the sagittae otolith size with the fish body size [ 24 , 27 ], the abundance of stranded organisms, and the causes of the stranding [ 27 , 29 , 30 ]. The upwelling of deep-water masses drags deep-sea organisms from their normal habitats.…”

“…Then, tidal currents and favorable wind conditions are the main mechanisms of mesopelagic fish stranding in the straits [ 28 ]. Battaglia et al [ 27 , 30 ] also reported that the phase of the moon promotes variability in both current strength and irradiance, thus affecting the vertical distribution of fishes.…”

Interactions between oceanographic variables and population structure of the yellowfin tuna Thunnus albacares (Bonnaterre, 1788) in the Western Central Atlantic

“…For the Mexican fleet targeting tuna with longlines operating in the Gulf of Mexico, larger catches occur during the new moon in comparison to the full moon (Fuentes et al, 2007; Madigan et al, 2021). This trend of CPUE variations among moon phases is directly related to the improvement of visualisation due to the highest lunar irradiance in the full moon in relation to the other phases (mainly the new moon); this fact allows the fish to explore deeper in the full moon, decreasing their CPUE in the upper depths and increasing their success in visual predation, preventing them from catching the hook; the opposite is seen in the first crescent, new moon and third crescent phases due to their lower lunar irradiance (Battaglia et al, 2022).…”

“…The findings demonstrated that Chla has an optimum peak for larger individuals of T. albacares at concentrations greater than where western transatlantic migration is to spawn and eastern is for feeding (Goñi & Arrizabalaga, 2010). of Africa and some parts of the Iberian Peninsula for feeding on herbivore fishes, omnivorous fishes and other invertebrates (Battaglia et al, 2022;Druyan & Fulakeza, 2014;Shih et al, 2014). This pattern of migration behaviour was also seen by Miller (2007) F I G U R E 1 0 Mean FL of T. albacares, per trimester (a-d) and represented in a graduated symbol shape (circle), projected on the SST spatialisation per trimester to ensure the sustainability of fishing activities (Coro et al, 2021;Hays et al, 2019).…”